Card and picture mounts have been available for many years and early patents such Hutton U.S. Pat. No. 739,315 and Butler U.S. Pat. No. 1,356,693 illustrate mounts which are positioned in a slot in the frame.
Dexter U.S. Pat. No. 1,410,555, Milmoe U.S. Pat. No. 1,493,159, Riley U.S. Pat. No. 1,999,423, Rado Re 19,983 and Engel U.S. Pat. No. 2,085,187 show typical corner mounts using an adhesive to secure the mount to the frame.
None of the above references deal with reinforcing the entrance of the mount which becomes frayed and torn due to frequent insertion of new material.